“The president came out with a new budget today,” Mr. Romney said as the crowd in an outdoor amphitheatre boo-ed. “You have reason for that response. He unfortunately came out with another trillion dollar deficit.”

The president’s $3.8 trillion budget for the fiscal year starting Oct. 1 would send the projected deficit above $1 trillion in 2012 for the fourth straight year. That means Mr. Obama will have fallen short of his promise to cut the deficit in half by the end of his first term.

Mr. Romney joined the chorus of Republicans Monday who criticized the president for failing to propose reforms to Medicare and Social Security, calling them among the most important parts of the nation’s safety net.

“This president miraculously today, with his new budget, had nothing to say about making sure that those programs are solvent and permanent,” Mr. Romney said. “If I’m president I will save Social Security and Medicare.”

The candidate also took swipes at his GOP opponents Newt Gingrich and Rick Santorum (without calling them out by name) for their long tenures in Washington.

“The challenge that we have in Washington is that people go there and they get infected by this Washington disease, which makes them think that government is a source of our greatness,” Mr. Romney said.

He touted his business background and experience as governor of Massachusetts, insinuating that Messers. Gingrich and Santorum’s backgrounds leave them ill-prepared for the presidency.

“We elected in President Obama someone who’d never run anything,” Mr. Romney said. “We’re not going to do that in the Republican Party. Let’s not nominate someone who hasn’t done anything and has not been a leader.”

After focusing nearly his entire campaign on Mr. Obama’s record, Mr. Romney has recently shifted his tone, saying it’s time to reveal more about the conservative alternative.

“This election is about more than just replacing President Obama,” Mr. Romney told the crowd. “People are going to ask, ok, we’re disappointed with him but where are you? Where are the conservatives going to lead?”

So far the front-runner has mainly divulged more about his biography and relatively little about his path forward. Monday evening Mr. Romney promised to use the Constitution as a blueprint and spent a hefty portion of his speech talking about his grandparents and his late father, George Romney, who grew up poor but eventually became the governor of Michigan.

To be sure, Mr. Romney arguably has the most detailed policy proposals of anyone in the GOP field. His 59-point economic plan includes a corporate tax cut, a harsher line with China and reductions in federal spending. But many of his prescriptions are for moderate or gradual changes, leaving some pockets of the base pressing Mr. Romney to show more passion and meatier policies to rally conservatives.

About Washington Wire

Washington Wire is one of the oldest standing features in American journalism. Since the Wire launched on Sept. 20, 1940, the Journal has offered readers an informal look at the capital. Now online, the Wire provides a succession of glimpses at what’s happening behind hot stories and warnings of what to watch for in the days ahead. The Wire is led by Reid J. Epstein, with contributions from the rest of the bureau. Washington Wire now also includes Think Tank, our home for outside analysis from policy and political thinkers.